In the field of semiconductor device fabrication, it is common to utilize insulation layers to separate conductive layers. Silicon nitride layers applied by plasma-enhanced chemical vapor deposition (PECVD) have been used as such inter-layer insulation films. These silicon nitride films have good insulation characteristics as well as high blocking effects against moisture and alkali metal ions. In addition, silicon nitride insulation layers exhibit conformal step coverage and high cracking resistance characteristics. See M. Maeda and T. Makino, Japanese Journal of Applied Physics 26:660-665 (1987).
However, there are some drawbacks to silicon nitride insulation layers. Such drawbacks include a relatively high dielectric constant compared with phosphorous-silicate glass (PSG) and silicon dioxide insulation layers, leading to relatively large parasitic capacitance and relatively long propagation delay times between devices. See M. Maeda and T. Makino.
A need for other dielectric or insulation film materials with low dielectric constants, conformal step coverage characteristics, good insulation characteristics, and high cracking resistance thus continued to exist. In response to this need, boron nitride films prepared by atmospheric chemical vapor deposition (CVD) or PECVD were devised. These boron nitride films were highly insulating, chemically inert, and thermally stable. The films also exhibit a low dielectric constant.
However, in order to be useful the boron nitride films must be compatible with current semiconductor device fabrication processes. Therefore, suitable etching techniques must be available.
Wet etching processes are common in semiconductor device fabrication processes. Common wet etchants include hydrofluoric acid (HF), buffered hydrofluoric acid (BHF), and hot phosphoric acid, for example. These etchants show little ability to etch boron nitride, and therefore current fabrication processes are not compatible with the use of boron nitride insulation layers.
A need thus exists for a method of etching boron nitride using conventional etchants so that boron nitride can be used in the fabrication of semiconductor devices. The ability to etch boron nitride will allow the material to be utilized, and allow one to take advantage of its favorable insulation layer characteristics.